A mirror used for a solar power generation system or a reflective member such as low-E glass often includes a glass substrate having a metal reflective film arranged thereon. However, a metal reflective film used for a reflective member typically has a problem of heat resistance. Therefore, a protective film is often formed on the metal reflective film for preventing the metal reflective film from being degraded by oxidization.
For example, there is proposed a material using a metal reflective film having a silica film sputtered as its top coating (see Patent Document 1). Although the silica film is used for improving scratch resistance of the material, the silica film does not have a high density because the silica film is formed by sputtering. Thus, its effect as a film for preventing oxidization of the metal film is considered to be low.
Further, Patent Document 2 proposes that the heat resisting property is important for a film that protects a layer from heat and that a silica film alone has an insufficient heat resisting property. Thus, Patent Document 2 proposes to use a mixed film having a silica film doped with aluminum oxide. However, Patent Document 2 does not teach or suggest using only a silica film as a protective film having a sufficient heat resisting property.
Patent Documents 3 and 4 propose to form a gas barrier layer by forming multiple layers of silica on a plastic substrate by using a plasma CVD method. However, a product using the gas barrier layer is not expected to be used in a high temperature environment because no material other than plastic is taught to be used as the substrate.